Coherent optical receiver device and coherent optical receiving method

Abstract

In a coherent optical receiver device, the dynamic range considerably decreases in the case of selectively receiving the optical multiplexed signals by means of the wavelength of the local oscillator light, therefore, a coherent optical receiver device according to an exemplary aspect of the invention includes a coherent optical receiver receiving optical multiplexed signals in a lump in which signal light is multiplexed; a variable optical attenuator; a local oscillator connected to the coherent optical receiver; and a first controller controlling the variable optical attenuator by means of a first control signal based on an output signal of the coherent optical receiver; wherein the coherent optical receiver includes a 90-degree hybrid circuit, a photoelectric converter, and an impedance conversion amplifier, and selectively detects the signal light interfering with local oscillation light output by the local oscillator out of the optical multiplexed signals; and the variable optical attenuator is disposed in the optical path of the optical multiplexed signals in a stage preceding the photoelectric converter, inputs the optical multiplexed signals, and outputs them to the coherent optical receiver controlling the intensity of the optical multiplexed signals based on the first control signal.

The invention claimed is: 
     
       1. An optical module, comprising:
 an optical light source configured to output a local oscillation light; 
 a variable optical attenuator configured to attenuate input multiplexed signals comprising a plurality of optical signals; 
 a coherent hybrid mixer configured to receive one of the plurality of optical signals by interfering with the local oscillation light; 
 a photoelectric converter configured to convert the received optical signal into a converted signal; 
 an electrical processing device configured to process an electrical signal, the electrical signal being downstream of the photoelectric converter; and 
 a controller configured to control an attenuation of the variable optical attenuator based on amplitude of the electrical signal, the controller configured to control the attenuation of the variable optical attenuator also based on optical intensity of the input multiplexed signals. 
 
     
     
       2. The optical module of  claim 1 , wherein the controller is further configured to control the attenuation of the variable optical attenuator based on amplifier gain for the electrical signal. 
     
     
       3. The optical module of  claim 1 , wherein the controller is further configured to control the attenuation of the variable optical attenuator based on a limit optical intensity of the photoelectric converter. 
     
     
       4. The optical module of  claim 1 , wherein the photoelectric converter comprises a photo diode. 
     
     
       5. The optical module of  claim 1 , wherein the controller is further configured to control the attenuation of the variable optical attenuator based on a limit electrical amplitude of the electrical signal. 
     
     
       6. The optical module of  claim 1 , further comprising:
 an optical splitter configured to obtain a part of the optical intensity of the input multiplexed signals; and 
 an optical power monitor configured to monitor the part of the optical intensity, 
 wherein the controller is further configured to control the attenuation based on the amplitude of the electrical signal and a monitoring result by the optical power monitor. 
 
     
     
       7. The optical module of  claim 1 , further comprising:
 a polarization optical splitter configured to split the input multiplexed signals into first polarization signals and second polarization signals; and 
 a second optical splitter configured to split the local oscillation light into a first split light and a second split light, 
 wherein the coherent hybrid mixer is further configured to receive one of the first polarization signals and one of the second polarization signals by interfering with the first split light and the second split light, respectively. 
 
     
     
       8. The optical module of  claim 1 , wherein the controller is further configured to control the attenuation of the variable optical attenuator so as to prevent the coherent hybrid mixer from receiving an excessive optical signal. 
     
     
       9. A method of receiving input multiplexed signals, the input multiplexed signals comprising a plurality of optical signals and the method comprising:
 outputting a local oscillation light; 
 attenuating the input multiplexed signals; 
 receiving one of the plurality of optical signals by interfering with the local oscillation light; 
 converting the received optical signal into a converted signal; 
 processing an electrical signal, the electrical signal being downstream of the converted signal; and 
 controlling an attenuation of the input multiplexed signals based on amplitude of the electrical signal and controlling the attenuation of the input multiplexed signals also based on optical intensity of the input multiplexed signals. 
 
     
     
       10. The method of  claim 9 , further comprising controlling the attenuation of the input multiplexed signals based on amplifier gain for the electrical signal. 
     
     
       11. The method of  claim 9 , further comprising control the attenuation of the input multiplexed signals based on a limit optical intensity of a photoelectric converter. 
     
     
       12. The method of  claim 9 , wherein the converting is performed using a photo diode. 
     
     
       13. The method of  claim 9 , further comprising controlling the attenuation of the input multiplexed signals based on a limit electrical amplitude of the electrical signal. 
     
     
       14. The method of  claim 9 , wherein the receiving is performing using a coherent hybrid mixer. 
     
     
       15. The method of  claim 9 , further comprising:
 obtaining a part of the optical intensity of the input multiplexed signals; 
 monitoring the part of the optical intensity; and 
 controlling the attenuation based on the amplitude of the electrical signal and a monitoring result. 
 
     
     
       16. The method of  claim 9 , further comprising:
 splitting the input multiplexed signals into first polarization signals and second polarization signals; 
 splitting the local oscillation light into a first split light and a second split light; and 
 receiving one of the first polarization signals and one of the second polarization signals by interfering with the first split light and the second split light, respectively. 
 
     
     
       17. The method of  claim 9 , further comprising controlling the attenuation of the input multiplexed signals so as to prevent input of excessive optical signal.